1. Field of the Invention
The present invention relates to a thermally-assisted magnetic head that records information while heating a magnetic recording medium to reduce coercive force of the magnetic recording medium.
2. Description of the Related Art
In recent years, for magnetic recording devices such as magnetic disk devices, etc., performance improvements of a magnetic head and a magnetic recording medium are demanded in accordance with high recording density. As the magnetic head, a composite-type magnetic head is widely used in which a reproducing head that has a magneto resistive effect element (MR element) for reading and a magnetic recording head that has an inductive-type electromagnetic transducer (a magnetic recording element) for writing are laminated on a substrate. In the magnetic disk devices, the magnetic head flies slightly above a surface of the magnetic recording medium.
The magnetic recording medium is a discontinuous medium on which magnetic microparticles gather. Each of the magnetic microparticles has a single magnetic domain structure. Of the magnetic recording medium, one recording bit is configured with a plurality of the magnetic microparticles. In order to increase the recording density, the asperity of a boundary of adjacent recording bits needs to be small. For this, the size of the magnetic microparticles needs to be small. However, when the size of the magnetic microparticles is small, thermal stability of the magnetization of the magnetic microparticles is also decreased due to the decrease in the volume of the magnetic microparticles. In order to solve this problem, increasing the anisotropy energy of the magnetic microparticles is effective. However, when the anisotropy energy of the magnetic microparticles is increased, the coercive force of the magnetic recording medium is also increased. As a result, it becomes difficult to record information using a conventional magnetic recording head. The conventional magnetic recording head has such a drawback, and this is a large obstacle to achieving an increase in the recording density.
As a method to solve this problem, a so-called thermally-assisted magnetic recording method has been proposed. In this method, a magnetic recording medium that has large coercive force is utilized. The magnetic field and heat are simultaneously applied to a portion of the magnetic recording medium to which information is recorded at the time of recording the information. Using this method, the information is recorded under a state where the temperature is increased and the coercive force is decreased in the information recording portion.
For thermally-assisted magnetic recording, a method in which a laser light source is utilized to heat the magnetic recording medium is common. Such a method has two types of methods: one method is to heat the magnetic recording medium by guiding laser light to a recording portion via a waveguide, etc. (a direct heating type); and the other method is to heat the magnetic recording medium by converting laser light to near-field light (a near-field light heating type). Near-field light is a type of electromagnetic field that is formed around a substance. Ordinary light cannot be tapered to a smaller region than its wavelength due to diffraction limitations. However, when light having an identical wavelength is irradiated onto a microstructure, near-field light that depends on the scale of the microstructure is generated, enabling the light to be tapered to a minimal region being approximately tens of nm in size. Since the thermally-assisted recording targets recording density region that requires selective heating only to the minimal region being approximately tens of nm, the near-field light heating type is preferred.
In U.S. Patent Application Publication No. 2008/205202, a configuration is disclosed in which a near-field-generator is disposed in a front part of a core of a waveguide through which light from a laser diode (LD) propagates.
As a concrete method for generating the near-field light, a method using a so-called plasmon antenna, which is a metal referred to as a near-field light probe that generates near-field light from light-excited plasmon, is common.
Direct irradiation of light generates the near-field light in the plasmon antenna; however, conversion efficiency of converting irradiated light into the near-field light is low with this method. Most of the energy of the light irradiated on the plasmon antenna reflects off the surface of the plasmon antenna or is converted into thermal energy. The size of the plasmon antenna is set to the wavelength of the light or less, so that the volume of the plasmon antenna is small. Accordingly, the temperature increase in the plasmon antenna due to that the light energy is converted into the thermal energy is significantly large.
The temperature increase causes volume expansion of the plasmon antenna, and the plasmon antenna protrudes from an air bearing surface (ABS) that is a surface facing the magnetic recording medium. Then, the distance between an edge part of the MR element on the ABS and the magnetic recording medium increases, causing a problem that servo signals recorded on the magnetic recording medium cannot be read during the recording process. Moreover, when the heat generation is large, the plasmon antenna may melt.
Currently, a technology is proposed in which light is not directly irradiated onto the plasmon antenna. For example, U.S. Pat. No. 7,330,404 discloses such a technology. In this technology, light propagating through a waveguide such as an optical fiber, etc. is not directly irradiated onto the plasmon antenna; however the light is coupled with a plasmon generator in a surface plasmon mode via a buffer portion to excite a surface plasmon in the plasmon generator. The plasmon generator includes a near-field-generator that is positioned on the ABS and that generates the near-field light. At the interface between the waveguide and the buffer portion, the light propagating through the waveguide completely reflects off, and light, which is referred to as evanescent light, is simultaneously generated that penetrates into the buffer portion. The evanescent light and a collective oscillation of charges in the plasmon generator are coupled, and the surface plasmon is then excited in the plasmon generator. The excited surface plasmon propagates to the near-field-generator along the plasmon generator, and then generates near-field light in the near-field-generator. According to this technology, since the light propagating through the waveguide is not directly irradiated to the plasmon generator, an excessive temperature increase of the plasmon generator is prevented.
U.S. Patent Application Publication No. 2010/103553 discloses a configuration in which a propagation edge is disposed in a plasmon generator that couples to light in a surface plasmon mode. The propagation edge that is an extremely narrow region is for propagating a surface plasmon generated in a plasmon generator to a near-field-generator positioned on an ABS.
In the thermally-assisted magnetic head that generates near-field light using evanescent light, a distance between a pole of an inductive-type electromagnetic transducer (magnetic recording element) for writing and a plasmon generator should be reduced to the extent possible to achieve high recording density. To achieve this, a configuration may be considered in which a dielectric body layer does not exist between the pole and the plasmon generator. However, with such a configuration, corrosion (oxidation) of the pole occurs due to contact and an electrical short between the pole and the plasmon generator. The pole loses its properties as a magnetic material when the pole is corroded, and thus the function of the magnetic recording element deteriorates.
U.S. Pat. No. 7,262,940 discloses a configuration in which an insulation film is disposed between a reproducing element and a recording element to separate them in order to suppress thermal deformation of the reproducing element in a magnetic head without thermal-assistance function. Similarly, JP Patent Application Publication No. H5-28430 discloses a configuration in which a pole is disposed in a recessed position relative to an alumina protecting film from an ABS in order to prevent a magnetic head from contacting the magnetic recording medium due to heat expansion of a pole of a magnetic recording element. U.S. Pat. No. 6,470,565 discloses a configuration in which a recession length (gap) of a magnetic head from other parts of a slider on an ABS is reduced. Since these magnetic heads are not configured for thermally-assisted magnetic recording, these configurations are not directed to suppress corrosion of the pole due to the contact of the plasmon generator and the pole of the magnetic recording element.
U.S. Patent Application Publication No. 2009/073597 discloses a configuration in which a heat dissipation film made of a material having a large thermal conductivity is disposed in the vicinity of a pole of a recording element. Additionally, the heat dissipation film is neither for preventing contact of the pole and a plasmon generator nor for preventing corrosion of the pole.